Those who don't know history are doomed to repeat it in summer school.

The Leica lens is a 50mm, while the Sony is a 55mm. As half a century proves, a tolerable 50 beats the best 55, every time.

Phorographers like "normal" lenses, where the focal length is about equal to the image diagonal. For the 35mm format, that's 43.3mm. Lenses around that focal length are easy to shoot, they're "transparent", with a very natural coverage.

Fast normals are difficult to build.

It's easier to build good fast lenses around 1.3x normal than true normal. So, the camera makers did what was "easier" in the late 50s and early 60s and make their f1.4 offerings 55 or 58mm lenses. The photographers, naturally, said "screw you". So, the camera makers tried 50mm. They were more expensive than the 55 or 58mm lenses, and they didn't perform as well, but photographers liked them better.